1. Field of the Invention
The present invention is directed to the field of dentistry, and is more specifically directed to a dental bridge system that may be secured between a natural tooth and an implant in such a manner so as to permit limited movement of the natural tooth and implant relative to one another.
2. Description of Related Art
Many patients require dental restorations or prostheses or a combination of dental restorations and prostheses to restore function or for aesthetic reasons. Some common dental restorations and prostheses include inlays, onlays, veneers, implants, crowns, bridges, and dentures. Depending on the patient's need, the dental restorations and prostheses can be removable or fixed. Dental restorations or dental prostheses provide the appearance of teeth and are constructed to mimic the function of teeth, such as masticating food and allowing for proper speech patterns.
One type of fixed or permanent dental restoration is an implant. Implants can replace an individual tooth or a combination of teeth and can support a crown, a bridge, or a denture. The implant functions as an artificial tooth root. The most common type of implant is secured in the bony tissue of the upper or lower jaw. Implants can also be secured on top of the jaw bone under the periosteum. Implants secured in the bony tissue of the upper or lower jaw are generally made out of titanium, titanium alloy, or some other medically compatible metal. A portion of the implant is screwed or tapped into a surgically prepared site in the bony tissue of the upper or lower jaw. The portion of the implant left exposed above the gumline can support a prosthesis such as a crown, a bridge, or a denture. Once the implant is in place, a process called osseointegration occurs. Osseointegration is when the bony tissue grows around the portion of the implant inserted in the jaw such that there is a structural and functional connection between the living bony tissue and the surface of the dental implant. After osseointegration has occurred, the portion of the implant inserted into the jaw is rigidly fixed in place by the bony tissue. The prosthesis can either be more or less permanently fixed to the implant or can be secured such that it is regularly removable.
Another type of dental restoration is a bridge. Bridges can be used to reduce the risk of gum disease, correct certain bite issues, improve speech, and replace missing teeth. Dental bridges are generally made up of at least two crowns. Crowns, also known as dental caps or tooth caps, are designed to cap the portion of a natural tooth at and above the gumline. Crowns essentially become the new visible portion of the tooth that can be used for chewing and allow for proper speech patterns. Crowns can also be made to fit over the portion of a dental implant left exposed above the gumline as described above. Crowns are generally made out of porcelain or dental ceramic, metal such as gold or other metal alloy, or a combination of porcelain and metal. Typically, dental bridges also have at least one artificial tooth, or pontic, fused between the two dental crowns.
Bridges containing pontics are a useful dental restoration option when multiple implants to restore multiple teeth cannot be used due to certain anatomical limitations or as a more cost effective treatment option. For example, when a patient loses a tooth in the lower jaw and the use of an implant would require inserting the implant in the lower jaw near the inferior alveolar nerve, there is a risk that inserting the implant could injure the nerve. If the missing tooth location is between two natural teeth or is between two dental implants, then a traditional dental bridge having a pontic can be used to restore the patient's missing teeth.
Another example of how bridges can be a particularly useful method of restoration is when the patient loses a tooth in the upper jaw below a sinus. As the bone where the missing tooth deteriorates through non-use, the sinus cavity expands into the space left by the bone, creating a pneumatized sinus. Normally, inserting an implant where there is a pneumatized sinus requires a sinus grafting procedure where the floor of the sinus is lifted by placing a bone graft, thereby creating adequate bony tissue to support the implant. This procedure is expensive and requires a six to twelve month recovery period. If the missing tooth space has a natural tooth on each side or a dental implant on each side, then a traditional dental bridge having a pontic can be used instead of an implant, thereby avoiding the sinus grafting procedure.
A traditional dental bridge cannot be anchored to both a natural tooth and an implant without significant risk. This is because natural teeth and dental implants respond differently to occlusal or compressive forces. The root of a natural tooth rests in a socket in the bony tissue of the jaw where it is attached and cushioned with periodontal ligament fibers. These fibers allow the natural tooth to move slightly in response to occlusal forces. The space between the tooth root and a wall of the bony tissue socket is roughly 0.25 mm. Normal, healthy physiologic lateral tooth mobility can range from less than 0.25 mm to more than 1 mm. After osseointegration, a dental implant is rigid relative to the bony tissue and cannot move in response to occlusal forces. A bridge anchored to a natural tooth on one side and to a dental implant on the other side is subjected to non-uniform stress during chewing and biting. This non-uniform stress can cause a structural failure on either end of the bridge.